1. Field of the Invention
The present invention belongs to the field of electronic computers in motor vehicles, and relates more particularly to the management by such computers of fluctuations of an electrical voltage supplied by an electrical power source of said electronic computers.
2. Description of the Related Art
Generally speaking, motor vehicle electronic computers are connected to the same power source, namely a battery of said motor vehicle.
Under normal operating conditions, the battery of a motor vehicle delivers a nominal electrical voltage generally of the order of 12 volts (V) (or 24 V). However, it is known that the electrical voltage supplied by such a battery fluctuates around the nominal value in particular according to the charge/discharge cycles of said battery, the wear of said battery, ambient temperature, etc.
For this purpose, in each electronic computer connected to the battery of the motor vehicle, an electrical power supply device is generally provided which supplies a regulated electrical voltage to the various electronic components of the electronic calculator from the fluctuating electrical voltage supplied by said battery.
These days, many motor vehicle electronic calculators use for their operation at least two electrical voltages with different regulated values. This is, for example, the case of the electronic computer controlling the operation of the motor vehicle engine, called an ‘engine control unit’.
In a known way, the engine control unit comprises a processor provided for operating with an electrical voltage regulated around a value V1, generally equal to 3.3 V, and peripherals for controlling motor vehicle engine actuators, provided for operating with an electrical voltage regulated around a value V2 greater than V1, generally equal to 5 V. Thus, the electrical power supply device of the engine control unit must supply two electrical voltages regulated around 3.3 V and 5 V respectively.
Such a need to have at least two electrical voltages regulated around different respective values is explained by a need to ensure that the control peripherals can effectively drive the various motor vehicle engine actuators, while reducing the electrical consumption of the engine control unit.
The control peripherals include output switches that drive motor vehicle engine actuators. These output switches are generally MOSFET transistors (Metal Oxide Semiconductor Field Effect Transistor, or an insulated gate field effect transistor), and require a gate-source electrical voltage of 5 V for ensuring that they are switched regardless of the driven actuator.
On the other hand, the electrical consumption of a processor decreases when the value of the electrical voltage supplying it decreases, which is why it is advantageous to have another electrical voltage regulated around a value V1 less than 5 V, e.g. equal to 3.3 V.
It is not uncommon, when the battery of the motor vehicle is worn and/or when the ambient temperature is very low (e.g. less than 10 degrees Celsius), that the value of the electrical voltage supplied by said battery becomes insufficient for the respective electrical power supply devices of the various electronic calculators to supply the electrical voltage regulated around 5 V.
This can occur particularly during the startup of the motor vehicle engine, since said startup requires a large electrical current from the battery, which may be accompanied by a temporary drop in the electrical voltage supplied by said battery to the respective electrical power supply devices of the various electronic computers.
For this purpose, the electrical power supply device of the engine control unit comprises a supervisory circuit which monitors the value of the electrical voltage supplied by the motor vehicle battery. When said value is too low to ensure that an electrical voltage regulated around 5 V is supplied, a first predefined alert signal, designated by ‘5V_reset’, is sent to the processor of the engine control unit. When the value of the electrical voltage supplied by the battery is too low to ensure that an electrical voltage regulated around 3.3 V is supplied, a second predefined alert signal, designated by ‘3.3V_reset’, is sent to said processor.
When the engine control unit processor receives a 5V_reset alert signal, the operation of said processor is interrupted in order to anticipate a possible loss of the electrical voltage regulated around 3.3 V. The control peripherals are also deactivated since, as the electrical voltage value of 5 V is no longer provided, it is not certain that their configuration can be maintained.
When the electrical voltage regulated around 5 V is again provided, the processor resets said control peripherals in order to ensure that they are correctly configured.
Clearly it follows then that there is a loss of functionality since the control of some actuators is no longer possible not only when the electrical voltage regulated around 5 V is not provided, but also temporarily after the 5 V regulated electrical voltage has been restored (owing to the aforementioned reset time).
However, some actuators like the starter relay must be activated for starting the motor vehicle engine. A loss of functionality is therefore problematic. This further proves all the more problematic for engines provided with an automatic ‘stop and start’ system.